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The objectives of this study were to report the long-term auditory results of prelinguistically deafened children with bilateral profound hearing impairment treated with a cochlear implant (CI); to analyze the role of auditory stimulation in the development of communicating abilities in early implanted children; and to define the limits of the auditory critical period. It was designed as a prospective cohort single-subject repeated-measures study of children with bilateral profound hearing impairment treated with a CI at a tertiary referral center with a pediatric CI program since 1991.

A total of 182 children with bilateral prelinguistic hearing impairment of profound degree treated with a Nucleus CI were enrolled in the study. Eighty-six children received a Nucleus 22 CI and 74 received a Nucleus 24. For data analyses the children were categorized by ages: 0-3 years of age (n = 94); 4-6 years (n = 36); 7-10 years (n = 30); 11-14 years (n = 22). The children were evaluated with a protocol that included tests of audition and speech perception, with closed-set (Vowel Confusion test, Series of Daily Words) and open-set tests (e.g. bisyllables, CID Sentences, CID Sentences adapted for children). Pure-tone averages significantly improved for all children in all groups with the CI compared with preoperative values. Nevertheless, only children implanted before the age of 6 years developed a high ability for recognition of bisyllables and sentences in an open-set. Results show that the earlier the implantation is undertaken, the better the performance outcome. Children implanted outside of the auditory critical period demonstrated significantly poorer performance, suggesting the occurrence of irreversible changes in the central auditory system.

In conclusion, eligible children should receive a CI as soon as bilateral profound hearing impairment is diagnosed. This usually permits them to achieve high-performance levels on speech and language measures and potentially integration into an oral communication environment.